Heretofore, many compounds such as chromomycin-type compounds, olivomycin-type compounds, and mithramycin-type compounds have been reported as anti-tumor antibiotics belonging to the group of aureolic acids [CRC Handbook of Antibiotic Compounds, CRC Press, vol. 1, 325-348, U.S.A. (1981)].
Chromomycin A.sub.3 is known which has a skeleton related to the present compound and which is represented by the following formula (A) [Tetrahedron, 23, 421 (1967)]. ##STR2##
It is known that these aureolic acids form dimeric complexes having divalent metal ions, e.g., 1/2 magnesium salt [Biochemistry, 28, 751 (1989); 32, 463 (1993); 32, 6588 (1993)].